Clinical Applications of Radiofrequency Lesioning for Back and Neck Pain
Radiofrequency (RF) neuroablation, or lesioning, is a target-specific, safe, and effective treatment used to prevent nociceptive signals from reaching the central nervous system, thereby providing long-lasting pain relief. The procedure has been used successfully as a treatment for a variety of conditions including facet-mediated pain, radiculopathies, and sacroiliac (SI) joint dysfunction. This article reviews the difference between continuous and pulsed RF lesioning, and explores the clinical evidence for their use in the treatment of back and neck pain.
What Is RF Lesioning?
The widespread use of RF current for the treatment of spinal pain began in 1980, when Sluijter and Metha introduced a 22-gauge cannula through which a thermocouple probe could be inserted.1,2 The smaller electrode meant that the procedure could be performed percutaneously on a conscious patient without causing much discomfort. This development was important because it allowed the patient to be monitored for complications. Shortly after the introduction of the Sluijter-Metha cannula (SMK) needle, a series of studies was published on the use of RF current for the treatment of facet joint pain, discogenic pain, SI joint pain, and sympathetically mediated pain.2-11 RF lesioning has since supplanted the use of other neurolytics (particularly chemical neurolytics), largely because of the highly focused nature of RF lesions.
Continuous vs Pulsed RF Lesioning
Radiofrequency energy can be applied either continuously or as pulsed currents. Continuous RF current generates heat in the tissue surrounding the electrode. On a pathologic level, the heat results in wallerian degeneration of the targeted nerves,12-15 while on a physiologic level, the current destroys all fiber types within a nerve and is not selective for any one fiber type.16-18 Coagulation occurs in a small, distinct oval pattern around the active tip of the needle—extending a distance of about 1.6 needle widths. Little coagulation occurs distal to the tip.
Additionally, studies have shown the volume of the lesion increases in relation to increasing tissue temperature, the duration of coagulation, and the dimensions of the active tip. For example, the size of the lesion increases proportional to an increase of temperature until the tissue temperature reaches 90oC; after this point, there is a risk of charring the tissue, which may cause cavitation and possible sterile abscess formation. Likewise, as the time of lesioning is prolonged, the volume of coagulation increases. Maximal size is achieved at 90 seconds; and at 60 seconds, 94% of maximal size is obtained. Similarly, a greater coagulation occurs with larger gauge active tips. These studies support the conclusion that optimal coagulation occurs when the tissue is treated for 60 to 90 seconds at 90oC with an 18- to 20-gauge needle. The placement of the active tip of the needle should be parallel to the nerve to allow greatest coagulation to occur; additionally, as exact placement of the nerve may vary from patient to patient, multiple lesioning should be performed to account for varied anatomy.
In contrast to continuous RF, pulsed RF (PRF) lesioning does not depend on heat to provide the therapeutic effect; rather, it uses the electrical field produced by the alternating current. Studies have shown that this electrical field can produce similar palliative effects resulting from a continuous RF lesion; although, an exact reasoning as to what occurs to produce such an effect is not fully understood.1,2 During PRF, intervals of short bursts of current lasting 20 milliseconds followed by a quiet phase of 480 milliseconds produce an intense electrical field while keeping the tissue temperature below neurolytic levels. Because temperature during PRF lesioning will not cause coagulation, PRF lesioning can be applied to the dorsal root ganglion (DRG) of a nerve to treat radiculopathies. The greatest electrical field occurs distal to the active tip and is greatest when voltage and current are as high as possible without tissue temperature exceeding 42 to 45oC (neurolytic level). Therefore, needle placement should be perpendicular to the DRG.
Lumbar Medial Branch RF
RF lesioning is gaining acceptance as an effective treatment option for the management of facet joint pain when more conservative approaches fail to provide symptomatic relief. Patients with facet joint pain commonly present with a deep, aching sensation in the low back that radiates in a nondermatomal pattern to the buttocks, the posterior or anterior thigh above the knee, the groin, and the hip. These patients often report morning stiffness. Younger patients may report that the pain followed some type of trauma, but older patients report an insidious onset. Although the diagnosis is more common in patients older than 65 years, it cannot be made solely on the basis of history, physical examination, or laboratory studies—such as radiographs.1,16,19,20 However, certain clinical features have been found to predict a positive response to medial branch block. These include pain relieved by lying down and meeting four of the following six characteristics: age greater than 65 years and back pain not exacerbated by forward flexion, rising from flexion, hyperextension, extension and rotation, or coughing.1,16,19
Mechanical pain must be distinguished from radicular pain. Radicular pain travels in a narrow band in the affected extremity. The pain is typically described as shooting or lancing, rather than dull or aching. It has both a deep and superficial quality, in that the patient feels both a deep and cutaneous sensation in the affected extremity. This pain is more often felt below, rather than above, the knee.21 Among patients with a mechanical cause of pain, the severity of the lower extremity pain mirrors that of the back pain; it never occurs independent of back pain. When attempting to distinguish between these two causes of pain, it is helpful to quantify the percentage of pain in the back versus that in the lower extremity. Of the pain in the lower extremity, one must distinguish between the percentage of pain above the knee and that below it.
Upon physical examination, the patient may report focal tenderness over the facet joints, and extension or lateral side bending may increase the pain.16,22-26 Patients with only facet joint pain have a normal neurologic examination. Imaging studies may show a normal-looking facet joint, although some patients show degenerative changes of the discs and facet hypertrophy.3,16,25,26